When there are too many entries defined in Windows Path environment variable, you might be faced with this error using the UI when adding a new entry. One solution without having to remove any existing entries is to use the PowerShell snippet below.

For example, to add “C:\Program Files\Java\jdk-14.0.2\bin” to Path :

• Open up Powershell in Administrator mode
• Enter the following:

$newPath = $env:Path + ';
C:\Program Files\Java\jdk-14.0.2\bin;'
[Environment]::SetEnvironmentVariable("Path", $newPath, "Machine")
$env:Path = $newPath

Source: Code Examples